1. Field of the Invention
The present invention relates to a complementary metal-oxide semiconductor (CMOS) image sensor and a method for fabricating the same, and more particularly, to a CMOS image sensor and a method for fabricating the same in which a metal barrier is formed to surround a periphery of a photodiode region so as to reduce loss of light that transmits through a microlens, thereby improving light-receiving efficiency of the photodiode region.
2. Discussion of the Related Art
Generally, a CMOS image sensor employs a switching mode that sequentially detects outputs of unit pixels using MOS transistors. The MOS transistors are formed in a semiconductor transistor to correspond to the number of unit pixels using CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. That is, to display images, the CMOS image sensor sequentially detects the electrical signals of the respective unit pixels in the switching mode by forming a photodiode and MOS transistors in each unit pixel.
Since the CMOS image sensor uses CMOS technology, it has advantages in that low power consumption is required and process steps are simplified due to a relatively small number of photo processes. Also, the CMOS image sensor has an advantage in that a control circuit, a signal processing circuit, and an analog-to-digital converter can be integrated in one chip to easily obtain a slim sized device.
FIG. 1 is a structural sectional view illustrating incident light to a photodiode region in a related art CMOS image sensor.
As shown in FIG. 1, the related art CMOS image sensor includes a semiconductor substrate 10 including a photodiode region 10a, a device isolation film 11 formed in the semiconductor substrate 10 to isolate devices from each other, a gate electrode 21 formed on a transistor region of the semiconductor substrate 10, source and drain regions 12 formed in the semiconductor substrate 10 at both sides of the gate electrode 21, an interlayer dielectric layer 20 formed on an entire surface of the semiconductor substrate 10 including the gate electrode 21, a first metal line 40 formed on the interlayer dielectric layer 20, a first contact 30 formed in the interlayer dielectric layer 20 to electrically connect the gate electrode 21 with the first metal line 40, an inter-metal dielectric layer 50 formed on an entire surface of the interlayer dielectric layer 20, a second metal line 70 formed on the inter-metal dielectric layer 50, a second contact 60 formed in the inter-metal dielectric layer 50 to electrically connect the first metal line 40 with the second metal line 70, an oxide layer 80 formed on the inter-metal dielectric layer 50 including the second metal line 70, a nitride layer 90 formed on the oxide layer 80, and a microlens 100 formed on the nitride layer 90 to condense light.
The aforementioned related art CMOS image sensor condenses light through the microlens 100 and transfers the condensed light to the photodiode region 10a of the semiconductor substrate 10 such that the condensed light is stored as an electrical signal in the photodiode region 10a. Therefore, a focal plane of the microlens 100 serves as a main factor that determines low illumination characteristics of the CMOS image sensor.
However, the related art CMOS image sensor has a drawback. If the focus of the microlens 100 is not exact, loss of the light condensed by the microlens 100 may occur. That is, as shown in FIG. 1, if the distance between the microlens 100 and the photodiode region 10a is longer than the originally designed distance, or if the focal distance of the microlens 100 becomes shorter than intended without being uniformly maintained, the light condensed by the microlens 100 may partially be beyond the photodiode region 10a, thereby causing loss of the light.